method

sequential_maintenance

v8.1.1 - Show latest stable - Class: ActiveRecord::ConnectionAdapters::ConnectionPool

sequential_maintenance(candidate_selector, &maintenance_work)

private

Perform maintenance work on pool connections. This method will select a connection to work on by calling the candidate_selector proc while holding the pool lock. If a connection is selected, it will be checked out for maintenance and passed to the maintenance_work proc. The connection will always be returned to the pool after the proc completes.

If the pool has async threads, all work will be scheduled there. Otherwise, this method will block until all work is complete.

Each connection will only be processed once per call to this method, but (particularly in the async case) there is no protection against a second call to this method starting to work through the list before the first call has completed. (Though regular pool behavior will prevent two instances from working on the same specific connection at the same time.)

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 940
        def sequential_maintenance(candidate_selector, &maintenance_work)
          # This hash doesn't need to be synchronized, because it's only
          # used by one thread at a time: the +perform_work+ block gives
          # up its right to +connections_visited+ when it schedules the
          # next iteration.
          connections_visited = Hash.new(false)
          connections_visited.compare_by_identity

          perform_work = lambda do
            connection_to_maintain = nil

            synchronize do
              unless self.discarded?
                if connection_to_maintain = @connections.select { |conn| !conn.in_use? }.select(&candidate_selector).sort_by(&:seconds_idle).find { |conn| !connections_visited[conn] }
                  checkout_for_maintenance connection_to_maintain
                end
              end
            end

            if connection_to_maintain
              connections_visited[connection_to_maintain] = true

              # If we're running async, we can schedule the next round of work
              # as soon as we've grabbed a connection to work on.
              @async_executor&.post(&perform_work)

              begin
                maintenance_work.call connection_to_maintain
              ensure
                return_from_maintenance connection_to_maintain
              end

              true
            end
          end

          if @async_executor
            @async_executor.post(&perform_work)
          else
            nil while perform_work.call
          end
        end

sequential_maintenance

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